使用sql server 2005中的一个公用表从多个表中选择数据

Question

我有许多表和一个公共表，其中包含所有这些表的 ID 例如：

表1

| ID | VALUE |       DATE |
---------------------------
|  1 |   200 | 25/04/2013 |
|  2 |   250 | 26/05/2013 |

表2

| ID | VALUE |       DATE |
---------------------------
|  1 |   300 | 25/05/2013 |
|  2 |   100 | 12/02/2013 |

表3

| ID | VALUE |       DATE |
---------------------------
|  1 |   500 | 5/04/2013  |
|  2 |   100 | 1/01/2013  |

还有一张普通的桌子

| ID |  TABLE | TABLEID |
-------------------------
|  1 | table1 |       1 |
|  2 | table3 |       1 |
|  3 | table2 |       1 |
|  4 | table1 |       2 |
|  5 | table2 |       2 |
|  6 | table3 |       2 |

使用这个公用表，我需要选择以上 3 个表中的所有数据 例如：

output
id    table   tableid   value    date
1     table1  1         200      25/04/2013
2     table3  1         500      5/04/2013
3     table2  1         300      25/05/2013
4     table1  2         250      26/05/2013
5     table2  2         100      12/02/2013
6     table3  2         100      1/01/2013

Answer 1

如果您不想使用UNION ALL，您可以使用COALESCE，同样使用LEFT JOIN，如下所示：

SELECT c.* 
     , COALESCE(t1.Value, t2.Value,t3.Value) AS Value
     , COALESCE(t1.Date, t2.Date,t3.Date) AS Date
  FROM Common c
  LEFT JOIN Table1 t1 ON c.tableid = t1.[id]
   AND [Table] = 'table1'
  LEFT JOIN Table2 t2 ON c.tableid = t2.[id]
   AND [Table] = 'table2'
  LEFT JOIN Table2 t3 ON c.tableid = t3.[id]
   AND [Table] = 'table3'
ORDER BY ID;

见this SQLFiddle

通过这种方式，您可以减少使用UNION ALL 连接所有记录的任务。但是对于给定的数据结构，无论如何您都必须连接所有表。

Answer 2

您可以UNION ALL在进程中添加标志列的表，然后将结果与普通表JOIN。

WITH CTE_Tables AS 
(
   SELECT 'Table1' AS Tab, * FROM Table1
   UNION ALL
   SELECT 'Table2' AS Tab, * FROM Table2
   UNION ALL
   SELECT 'Table3' AS Tab, * FROM Table3
)
SELECT * 
FROM CommonTable c1 
LEFT JOIN CTE_Tables cte ON cte.ID = c1.TableID AND cte.Tab = c1.[Table]

SQLFiddle DEMO

Answer 3

您需要分别使用common 表连接所有表，然后使用UNION ALL 连接它们：

SELECT *
  FROM Common c
  JOIN Table1 t1 ON c.tableid = t1.[id]
   AND [Table] = 'table1'
UNION ALL
SELECT *
  FROM Common c
  JOIN Table2 t2 ON c.tableid = t2.[id]
   AND [Table] = 'table2'
UNION ALL
SELECT *
  FROM Common c
  JOIN Table3 t3 ON c.tableid = t3.[id]
   AND [Table] = 'table3';

见this SQLFiddle